<!DOCTYPE html>
<html>

<head>
    <meta charset="utf-8">
    <title>菜鸟教程(runoob.com)</title>
</head>

<body>

    <p>点击这个按钮，获得基于时间的问候。</p>
    <button onclick="myFunction()">点击这里</button>
    <p id="demo"></p>
    <script>
        function myFunction() {
            var x = "";
            var time = new Date().getHours();
            if (time < 20) {
                x = "Good day";
            }
            else {
                x = "Good evening";
            }
            document.getElementById("demo").innerHTML = x;
        }
    </script>

</body>

</html>